U.S. patent application number 10/173191 was filed with the patent office on 2003-02-13 for method and apparatus for transmitting user data in an hsdpa mobile communication system.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Chang, Jin-Weon, Choi, Sung-Ho, Kim, Seong-Hun, Lee, Hyeon-Woo, Lee, Kook-Heui.
Application Number | 20030031119 10/173191 |
Document ID | / |
Family ID | 19710943 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030031119 |
Kind Code |
A1 |
Kim, Seong-Hun ; et
al. |
February 13, 2003 |
Method and apparatus for transmitting user data in an HSDPA mobile
communication system
Abstract
Transmitting user data in an HSDPA (High Speed Downlink Packet
Access) mobile communication system by using an FCS (Fast Cell
Selection) technique where an RNC (Radio Network Controller)
transmits packet data only to a Node B that is best able to
transmit data to a UE (User Equipment) on the downlink.
Inventors: |
Kim, Seong-Hun; (Seoul,
KR) ; Lee, Hyeon-Woo; (Suwon-shi, KR) ; Lee,
Kook-Heui; (Songnam-shi, KR) ; Choi, Sung-Ho;
(Songnam-shi, KR) ; Chang, Jin-Weon; (Yongin-shi,
KR) |
Correspondence
Address: |
Paul J. Farrell, Esq.
DILWORTH & BARRESE, LLP
333 Earle Ovington Blvd.
Uniondale
NY
11553
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
KYUNGKI-DO
KR
|
Family ID: |
19710943 |
Appl. No.: |
10/173191 |
Filed: |
June 17, 2002 |
Current U.S.
Class: |
370/200 |
Current CPC
Class: |
H04L 1/0003 20130101;
H04W 24/00 20130101; H04L 1/1812 20130101; H04L 1/0009 20130101;
H04W 36/08 20130101; H04W 76/10 20180201; H04L 1/0025 20130101;
H04W 92/12 20130101; H04W 48/08 20130101; H04L 1/0026 20130101 |
Class at
Publication: |
370/200 |
International
Class: |
H04L 005/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2001 |
KR |
34177/2001 |
Claims
What is claimed is:
1. A method of transmitting user data to a UE (User Equipment) in a
mobile communication system where the same RNC (Radio Network
Controller) controls a first Node B, which is currently providing a
service to the UE, and at least one neighboring Node B, the UE
capable of receiving signals from the first Node B and the at least
one neighboring Node B, the method comprising the steps of:
establishing a transmission link with a new Node B based on channel
status information of the first Node B and the at least one
neighboring Node B received from the UE by the RNC; monitoring the
channel statuses of the first Node B and the at least one
neighboring Node B and transmitting an identification (ID) of the
best cell Node B based on the channel status to the first Node B
and the at least one neighboring Node B by the UE; transmitting a
BCSI (Best Cell Switching Indicator) to the RNC by the at least one
neighboring Node B if the best cell Node B ID is identical to the
ID of one of the at least one neighboring Node B; and transmitting
user data on the transmission link to the best cell Node B being
the one of the at least one neighboring Node B by the RNC.
2. The method of claim 1, wherein the new Node B is the one of the
at least one neighboring Node B from which the UE receives a
signal.
3. The method of claim 1, wherein the channel statuses of the first
Node B and the at least one neighboring Node B are estimated by
measuring the reception strengths of CPICHs (Common Pilot Channels)
received from the first Node B and the at least one neighboring
Node B.
4. The method of claim 1, wherein the best cell Node B ID is coded
in a BCI (Best Cell Indicator) field of a DPCCH (Dedicated Physical
Control Channel).
5. The method of claim 1, wherein upon receipt of the BCI, the RNC
transmits user data only to the at least one neighboring Node B
being the new best cell Node B, and discontinues transmission to
the first Node B being the old best cell Node B.
6. An apparatus for transmitting user data to a UE (User Equipment)
in a mobile communication system, comprising: a first Node B
currently providing a service to the UE, the UE for transmitting
channel status information of the first Node B and at least one
neighboring Node B, monitoring the channel statuses of the first
Node B and the at least one neighboring Node B, and transmitting
the identification (ID) of the best cell Node B based on the
channel status to the first Node B and the at least one neighboring
Node B, the at least one neighboring Node B for transmitting a BCSI
(Best Cell Switching Indicator) if the best cell Node B ID is
identical to the ID of one of the at least one neighboring Node B;
and an RNC (Radio Network Controller) for establishing a
transmission line with a new Node B based on the channel status
information received from the UE and transmitting user data on the
transmission link to the best cell Node B.
7. The apparatus of claim 6, wherein the new Node B is the one of
the at least one neighboring Node B from which the UE receives a
signal.
8. The apparatus of claim 6, wherein the channel statuses of the
first Node B and the at least one neighboring Node B are estimated
by measuring the reception strengths of CPICHs (Common Pilot
Channels) received from the first Node B and the at least one
neighboring Node B.
9. The apparatus of claim 6, wherein the best cell Node B ID is
coded in a BCI (Best Cell Indicator) field of a DPCCH (Dedicated
Physical Control Channel).
10. The apparatus of claim 6, wherein upon receipt of the BCI, the
RNC transmits user data only to the one of the at least one
neighboring Node B being the new best cell Node B, and discontinues
transmission to the first Node B being the old best cell Node B.
Description
PRIORITY
[0001] This application claims priority to an application entitled
"Method and Apparatus for Transmitting User Data in an HSDPA Mobile
Communication System" filed in the Korean Industrial Property
Office on Jun. 16, 2001 and assigned Serial No. 2001-34177, the
contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to a packet data
transmitting apparatus and method in an HSDPA (High Speed Downlink
Packet Access) mobile communication system, and in particular, to
an apparatus and method for transmitting packet data from an RNC
(Radio Network Controller) only to the best cell for a UE (User
Equipment) using FCS (Fast Cell Selection).
[0004] 2. Description of the Related Art
[0005] HSDPA is a generic term that refers to data transmission
schemes that bring high-speed data delivery to terminals by means
of HS-DSCHs (High Speed-Downlink Shared Channels) and their related
control channels in an asynchronous mobile communication system
(hereinafter, referred to as UMTS: Universal Mobile
Telecommunications System). To support HSDPA, AMC (Adaptive
Modulation and Coding), HARQ (Hybrid Automatic Retransmission
Request), and FCS have been proposed.
[0006] With reference to FIG. 1, a typical UMTS mobile
communication system will be described along with the AMC, HARQ,
and FCS.
[0007] Referring to FIG. 1, the UMTS mobile communication system
includes a core network 100, a plurality of RNSs (Radio Network
Sub-systems) 110 and 120, and a UE 130. Each RNS is comprised of an
RNC 111 or 121, and a plurality of Node Bs 113 & 115 or 123
& 125. The RNCs 111 and 121 are categorized into a serving RNC
(SRNC), a drift RNC (DRNC), or a controlling RNC (CRNC) according
to their functions. An SRNC manages UE information and takes charge
of data transmission between a UE and the core network. If data
from the UE is delivered to the SRNC via an RNC other than the
SRNC, the RNC is called a DRNC. A CRNC of a Node B is an RNC that
controls the Node B. For example, if the RNC 121 manages the
information of the UE 130, the RNC 121 is an SRNC. When data from
the UE 130 is delivered to the RNC 121 via the RNC 111, the RNC 111
is the DRNC of the UE 130. The RNC 121 acts as the CRNC of the Node
Bs 123 and 125.
[0008] AMC: This is a technique for adapting the modulation and
coding format based on the received signal quality of the UE 130
and the channel condition between a particular Node B and the UE
130 to increase the use efficiency of the entire cell. Therefore,
the AMC involves a plurality of modulation and coding schemes
(MCSs). MCSs can be defined from level 1 to level n. In other
words, the AMC is an adaptive selection of an MCS level according
to the channel condition between the UE 130 and the serving Node
B.
[0009] n-channel SAW HARQ (n-channel Stop And Wait HARQ) as a kind
of HARQ: Two techniques are introduced to increase typical ARQ
efficiency. That is, a retransmission request and a response for
the retransmission request are exchanged between the UE 130 and the
Node B, and defective data is temporarily stored and combined with
corresponding retransmitted data.
[0010] FIG. 2 illustrates a HARQ-based retransmission between the
UE 130 and the Node B 123, and an RLC (Radio Link Control)
ARQ-based retransmission between the UE 130 and the SRNC 121, which
is currently under discussion as functionality sharing between the
SRNC 121 and the Node B 123 in HSDPA.
[0011] Referring to FIG. 2, the UE 130 and the Node B 123 each are
additionally provided with layers called a MAC-h 201 and a MAC-h
205 to support AMC, HARQ and FCS. The MAC-h 205 takes charge of
scheduling, MCS assignment and HARQ processing for a particular UE.
Therefore, a general ARQ functionality exists between an RLC 207 of
the SRNC 121 and an RLC 203 of the UE 130, and an HARQ
functionality between the MAC-h 205 of the Node B 123 and the MAC-h
201 of the UE 130.
[0012] Specifically, since RLC retransmission occurs between the
SRNC 121 and the UE 130, a long time is required for transmitting a
retransmission request and a response for the retransmission
request. On the other hand, a retransmission request and a response
for the retransmission request based on HARQ between the UE 130 and
the Node B 123 takes a relatively short time. Defective data are
immediately discarded in the RLC retransmission, whereas defective
data are temporarily stored and combined with corresponding
retransmitted data to thereby reduce an error probability in the
HARQ retransmission. The data are combined by chase combining (CC)
or incremental redundancy (IR). The same data is transmitted at an
initial transmission and a retransmission in the former method, and
different data are transmitted at the initial transmission and the
retransmission in the latter method.
[0013] FCS: When the UE 130 enters a soft handover region, it
selects the cell that is best able to transmit the required data.
To support the FCS, an HS-DSCH FP (HS-DSCH Frame Protocol) is
defined for a lub interface between the Node B 123 and the SRNC 121
and for a lur interface between the SRNC 121 and the CRNC 111. The
functionalities and structure of the HS-DSCH FP, however, are yet
to be defined in detail.
[0014] The general operation of the HSDPA mobile communication
system will be described with reference to FIGS. 1 and 2.
[0015] When the UE 130 supporting HSDPA enters a soft handover
region defined as the overlapped region of the Node B 123 and the
Node B 125, it establishes radio links with the Node Bs 123 and
125. The cells of the Node Bs that have radio links with the UE 130
are the active set of the UE 130. Data delivery from only the best
cell in channel condition in the active set is FCS. The UE 130
periodically monitors the channel conditions with the cells 123 and
125 in the active set to check whether there is a cell better than
the present best cell. If such a cell is detected, the UE 130
transmits a Best Cell Indicator (BCI) to the cells 123 and 125 in
the active set to change the best cell. The BCI contains the
identification (ID) of the new best cell. Upon receipt of the BCI,
the cells 123 and 125 determine whether the BCI indicates them.
Then, the new best cell transmits an HSDPA packet to the UE 130 on
an HS-DSCH.
[0016] FCS is a technique assuming characteristics between a soft
handover and a hard handover that occur in conventional mobile
communication systems, to efficiently support the UE that changes
its serving cell. The soft handover is a technique in which the UE
maintains radio links with a plurality of Node Bs that send signals
with strengths at or above an acceptable level without
communication interruption between the UE and a UTRAN (UMTS Radio
Access Network). The soft handover offers the benefit of continuous
communication, but increases inter-cell interference. In contrast,
the hard handover allows only one radio link for the UE. Assuming
that the UE receives signals with strengths at or above an
acceptable level from cell A and cell B, and cell A is a serving
cell, if the signal from cell B satisfies a predetermined condition
(e.g., it is better than the signal from cell B), the UE releases
the radio link from cell A and establishes a new radio link with
cell B. The hard handover reduces interference but causes
communication interruption. While the FCS is similar to the hard
handover in allowing only one radio link between a UE and a UTRAN
and thus reducing interference, it reduces communication
interruption as compared to the hard handover. To implement the
FCS, the current proposed communication procedure is performed as
follows.
[0017] When the UE is in a soft handover region, it establishes
radio links with a plurality of cells and its SRNC transmits the
same data to Node Bs in the active set of the UE. The Node Bs store
the data in buffers for the case of being the best cell. When the
best cell is changed, that is, FCS is implemented, the new best
cell resumes a service with the UE using the stored data.
[0018] How the UE is wirelessly connected to the Node Bs in its
active set (active set Node Bs) will first be described. When the
UE is located in the soft handover region, an RRC (Radio Resource
Control) entity of the SRNC recognizes it by a Measurement Report
(MP) received from the UE. In general, the RRC entity transmits an
RRC message Active Set Update to the UE. The Active Set Update
message notifies the UE that it has entered the soft handover
region, providing information about radio links to be established,
so that the UE can receive downlink transmission on a plurality of
radio links. After establishing the radio links, the UE transmits
an Active Set Update Complete message to the RRC entity. FIG. 3
illustrates a signal flow for an RLC retransmission using FCS in a
typical CDMA (Code Division Multiple Access) communication
system.
[0019] Referring to FIGS. 1, 2 and 3, the RLC retransmission will
be described below on the assumption that the Node B 125 is an
active set Node B and the RNC 121 is the SRNC of the UE 130. It is
to be noted in the following description that an active set Node B
is a Node B other than the best cell Node B (BNB) in the active set
and the best cell Node B is a Node B in the active set which is
best able to receive a signal from the UE.
[0020] Once the UE 130 enters the soft handover region, the SRNC
121 recognizes it from a Measurement Report received from the UE
130 and determines to establish new radio links in step 301. This
implies that the active set of the UE 130 includes at least two
cells. The SRNC 121 transmits a Radio Link Setup Request message to
Node Bs in the active set by an NBAP (Node B Application Protocol)
in step 302. The Radio Link Setup Request message includes the IDs
of the cells to which to establish radio links, timing information
like frame offsets and chip offsets, and information needed to
establish the radio links such as scrambling codes for the uplink
and the downlink transmission, channelization codes, and
transmission power control information. In step 303, the Node B 125
being an active set Node B establishes a radio link using the
information included in the Radio Link Setup Request message and
transmits a Radio Link Setup Response message to the SRNC 121. The
Node B 125 receives data from the UE 130 on the uplink in step 304.
The SRNC 121 then establishes transmission lines for sending user
traffic on the lub interface by an ALCAP (Access Link Control
Application Part) being a transmission signaling protocol,
confirming that the radio links have been successfully established
in step 305. An FP of the SRNC 121 synchronizes transport channels
to the radio links in step 306 and transmits user data in a data
frame to all the Node Bs that have established the radio links in
step 307. The Node Bs 123 and 125 buffer the received user data in
step 308. The Node B 123, which is selected as the best cell,
starts data transmission to the UE 130 on its radio link and the
Node B 125 is in the state where it can send the buffered user
data. After preparing for data communication on the new radio
links, the SRNC 121 notifies the UE 130 of the completed
preparation for data communication by an Active Set Update message
in step 309. The Active Set Update message contains a scrambling
code and a channelization code for downlink transmission,
transmission power control information, and the IDs of Node Bs that
have established a radio link with the UE 130. In step 310, the UE
130 transmits an Active Set Update Complete message to the SRNC
121, notifying the receipt of the Active Set Update message. While
one Node B is an active set Node B in FIGS. 2 and 3, a plurality of
active set Node Bs may exist.
[0021] FIGS. 5 illustrates a signal flow for transmission of
messages and user data between the UE, the Node Bs, and the SRNC in
the case where the best cell is not changed.
[0022] Referring to FIG. 5, the physical layer (PHY) of the UE 130
transmits a BCI, a CQI (Channel Quality Indicator), and other
information on a DPCCH (Dedicated Physical Control Channel) in step
501. Since the cells in the active set are informed of the
scrambling code and channelization code of the DPCCH from the UE
130 in step 302 of FIG. 3, all the active set cells including the
best cell 123 receive the BCI. The BCI contains the coded logical
ID of the best cell that has the best radio link measured by the UE
130. The radio link status of a cell is estimated by measuring the
reception strength of a CPICH (Common Pilot Channel) from the cell.
The logical best cell ID is determined by agreement between the
SRNC 121 and the UE 130 during set-up of an HS-DSCH or by the
Active Set Update Complete message in step 309 of FIG. 3. Aside
from the BCI, the DPCCH may have other information such as
information about whether user data on the HS-DSCH has errors and
the radio link quality of the best cell. Here, the active set Node
B 125 checks whether the BCI indicates the Node B 125. If it does
not, the Node B 125 does not receive the other information. If the
BCI indicates the Node B 125, the Node B 125 transmits an MCS level
and a reception indicator to the UE 130 based on the CQI and the
ACK received from the UE. Since it is assumed that the best cell is
not changed in FIG. 5, the BCI indicates the Node B 123. In step
502, the Node B 123 receives the BCI and determines an MCS level
and user data to be transmitted based on the CQI and the ACK and
transmits the CQI and a reception indicator by scheduling. The
reception indicator indicates an action time of transmitting user
data. The Node B 123 transmits the user data at the action time in
step 503. In step 504, the UE 130 checks whether the received user
data has errors and transmits a BCI, a CQI, and an ACK to the Node
B 125. Steps 505 to 509 are a repetition of steps 501 to 504. In
steps 510 to 540, user data exchange and inter-Node B buffer
management occur in the SRNC 121, the Node B 125, and the Node B
123. The Node B 123 receives the user data from the SRNC 121 and
transmits it to the UE 130, while the Node B 125 simply buffers the
user data without transmitting it just for the case of being the
best cell. The Node B 123 notifies the Node B 125 of the
transmitted data so that the Node B 125 can discard the same data
as transmitted from its buffer.
[0023] FIGS. 6 illustrates a signal flow for transmission of
messages and user data between the UE, the Node Bs, and the SRNC in
the case where the best cell is changed. For convenience's sake, it
is assumed that an old best cell is the Node B 123, a new best cell
is the Node B 125, and the UE 130 periodically transmits a BCI and
determines to change the best cell from the Node B 123 to the Node
B 125 at an arbitrary time point.
[0024] To switch the best cell from the Node B 123 to the Node B
125, the UE 130 transmits a BCI indicating the Node B 125 in step
601. Since the Node Bs 123 and 125 have already known the
scrambling code and the channelization code for the uplink
transmission, they can receive the BCI and determine whether the
best cell is changed or not by checking the BCI. Thus, the Node B
123 neglects signals other than the BCI on the DPCCH, discontinuing
transmission of an HS-DSCH. The Node B 125 determines an
appropriate MCS by analyzing a CQI received from the UE 130 after
the BCI, preparing for data transmission. The UE 130 transmits EQS
(End Queue Status) information to the Node B 125 through its MAC-h
and PHY to notify the Node B 125 of its reception status in step
602. The EQS information can be transmitted on a DPCCH or a DPDCH
(Dedicated Physical Data Channel). In step 603, the Node B 125
determines what user data to send based on the EQS information and
transmits the determined MCS information including information
about the number of channelization codes to be used for data
transmission and OVSF position information to the UE 130. The Node
B 125 transmits the UE 130 the user data using the MCS in step 604.
Steps 605, 606 and 607 are a repetition of steps 601, 603 and 604
except that the best cell has been changed to the Node B 125.
Despite the change of the best cell, user data are exchanged and
inter-Node B buffer management is performed in steps 610 and 620 in
the same manner as steps 510 to 540 of FIG. 5.
[0025] As described above, once the UE 130 is located in the soft
handover region and the radio connection is completed, the SRNC 121
transmits data both to the best cell Node B and the active set Node
B. The best cell Node B discards data that has been transmitted
successfully from its buffer and notifies the active set Node B of
the transmitted data to discard the same data from the buffer.
[0026] If the best cell is changed, the UE reports its reception
status to the new best cell Node B by predetermined signaling. It
is proposed that the above procedure occur between the active set
Node B, the best cell Node B, and the MAC-h of the UE. The
inter-Node B buffer management requires a new signaling procedure
and assignment of IDs to MAC-h SDUs (Service Data Unit). The SDU
IDs are the sequence numbers (SNs) of the SDUs.
[0027] As described above, active set Node Bs discard user data
destined for the UE without transmitting it, resulting in
dissipation of buffer resources. For example, if four Node Bs
including the best cell Node B are in the active set, they will
store the same data. Yet, only the best cell Node B can send the
data to the UE, while the other Node Bs discard them.
[0028] Moreover, the SRNC transmits the same data to the best cell
Node B and the active set Node Bs but only the best cell Node B
transmits it to the UE, thereby causing unnecessary dissipation of
transmission resources between the SRNC and the Node Bs.
[0029] With regard to the inter-Node B buffer management, this is
performed to make the buffers of the best cell Node B and the
active cell nods B have the same data, increasing implementation
complexity. While the best cell Node B discards successfully
transmitted data, the active set Node Bs preserve the data because
they do not transmit the data.
[0030] Then the best cell Node B notifies the active set Node Bs of
the transmitted data so that they can discard the data from their
buffers. When the best cell is changed, the new best cell Node B
does not know the reception status of the UE. This implies that the
UE must report its reception status by some signaling. Considering
that this procedure happens in the active set Node Bs, the best
cell Node B and the MAC-h of the UE, the signaling can be MAC-h
signaling. The inter-Node B buffer management requires definition
of a new signaling procedure between the entities responsible for
the buffer management and assignment of IDs to MAC-h SDUs in the
form of SNs. The SN assignment to MAC-h SDUs increases
overhead.
SUMMARY OF THE INVENTION
[0031] It is, therefore, an object of the present invention to
provide a communication method and procedure for supporting FCS,
solving the above conventional problems.
[0032] It is another object of the present invention to provide an
apparatus and method for transmitting an FP data frame only to a
best cell Node B.
[0033] It is also another object of the present invention to
provide an apparatus and method for encouraging efficient use of
lub transmission resources and efficient use of buffer resources in
active set Node Bs.
[0034] It is a further object of the present invention to provide
an apparatus and method for enabling a Node B to report the change
of a best cell to an FP of its SRNC in order to minimize RLC
retransmission requests.
[0035] It is also a further object of the present invention to
provide an apparatus and method for efficiently managing an RLC
buffer for a UE by enabling fast transmission of an RLC
retransmission request when its best cell is changed.
[0036] It is still another object of the present invention to
provide an FCS apparatus and method for transmitting user data
using transmission resources efficiently at a fast cell selection
in an HSDPA mobile communication system.
[0037] It is also still another object of the present invention to
provide an apparatus and method for enabling an RNC to transmit
user data only to a best cell Node B at a fast cell selection in
order to efficiently use transmission resources in an HSDPA mobile
communication system.
[0038] It is yet another object of the present invention to provide
a method and apparatus for enabling each Node B to efficiently
manage its memory for storing data received from an RNC in an HSDPA
mobile communication system in which only a best cell Node B
transmits high-speed packet data to a UE using FCS.
[0039] To achieve the above and other objects, an RNC, which
controls a first Node B currently providing a service to a UE, the
UE capable of receiving signals from the first Node B and at least
one neighboring Node B, and the at least one neighboring Node B,
establishes a transmission line with a new communicable Node B
based on channel status information of the first Node B and the
neighboring Node B received from the UE. The UE monitors the
channel statuses with the first Node B and the neighboring Node B
and transmits the ID of the best cell Node B in channel status to
the first Node B and the neighboring Node B. The neighboring Node B
transmits a BCSI (Best Cell Switching Indicator) to the RNC if the
best cell Node B ID is identical to the ID of the neighboring Node
B. Then, the RNC transmits user data on the transmission line to
the best cell Node B being the neighboring Node B.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description when taken in conjunction with the
accompanying drawings in which:
[0041] FIG. 1 illustrates the configuration of a typical CDMA
mobile communication system;
[0042] FIG. 2 illustrates a protocol structure for an HSDPA mobile
communication system;
[0043] FIG. 3 is a diagram illustrating a signal flow for
transmission line establishment between a Node B and an RNC in a
typical HSDPA mobile communication system;
[0044] FIG. 4 is a diagram illustrating a signal flow for
transmission line establishment between a Node B and an RNC in an
HSDPA mobile communication system according to an embodiment of the
present invention;
[0045] FIG. 5 illustrates a user data transmission method after
establishment of transmission lines in the procedure of FIG. 3 in
the case where the best cell is not changed;
[0046] FIG. 6 illustrates a user data transmission method after
establishment of transmission lines in the procedure of FIG. 3 in
the case where the best cell is changed;
[0047] FIG. 7 illustrates a user data transmission method after
establishment of transmission lines in the procedure of FIG. 4 in
the case where the best cell is not changed;
[0048] FIG. 8 illustrates a user data transmission method after
establishment of transmission lines in the procedure of FIG. 4 in
the case where the best cell is changed;
[0049] FIG. 9A illustrates the structure of an FP data frame in the
HSDPA mobile communication system according to the embodiment of
the present invention;
[0050] FIG. 9B illustrates the structure of an FP control frame in
the HSDPA mobile communication system according to the embodiment
of the present invention;
[0051] FIG. 9C illustrates the structure of another FP control
frame in the HSDPA mobile communication system according to the
embodiment of the present invention;
[0052] FIG. 10 is a block diagram of an RNC controller for
transmitting user data by the FP in the HSDPA mobile communication
system according to the embodiment of the present invention;
[0053] FIG. 11 is a block diagram of an FP controller illustrated
in FIG. 10;
[0054] FIG. 12 is a block diagram of a Node B for transmitting user
data by the FP in the HSDPA mobile communication system according
to the embodiment of the present invention;
[0055] FIG. 13 is a flowchart illustrating a user data transmission
method in a UE in the HSDPA mobile communication system according
to the embodiment of the present invention;
[0056] FIG. 14 is a flowchart illustrating a user data transmission
method in the Node B in the HSDPA mobile communication system
according to the embodiment of the present invention; and
[0057] FIG. 15 is a flowchart illustrating a user data transmission
method in the RNC UE in the HSDPA mobile communication system
according to the embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0058] A preferred embodiment of the present invention will be
described herein below with reference to the accompanying drawings.
In the following description, well-known functions or constructions
are not described in detail since they would obscure the invention
in unnecessary detail.
[0059] The present invention is intended to have an RNC transmit
user data only to one of the Node Bs in the active set, i.e., the
best cell Node B for transmitting to a UE on the downlink using FCS
in an HSDPA mobile communication system. This leads to efficient
memory management for active set Node Bs and decreases unnecessary
signaling between the Node Bs and the RNC.
[0060] To achieve the goal, a newly defined transmission line setup
between a Node B and an RNC, user data transmission, an FP
structure, and the structures of the RNC and the Node B are
necessary.
[0061] A description will first be made of a transmission line
setup method between an RNC and a Node B according to an embodiment
of the present invention with reference to FIG. 4. The Node B is
one that should establish a new radio link with a UE when the UE
enters a soft handover region.
[0062] FIG. 4 is a diagram illustrating a signal flow for setting
up a transmission line for RLC retransmission using FCS in a CDMA
mobile communication system using HSDPA according to the embodiment
of the present invention. In FIG. 4, it is to be noted that Node Bs
that should establish radio links with the UE are connected to the
same RNC and the protocol entity of each node is marked with an
oval. The best cell Node B 123 is a Node B that takes charge of a
cell preserving a radio link before the UE 130 enters the soft
handover region, and the active set Node B is a Node B that takes
charge of a cell to establish a new radio link along with the
entrance of the UE 130 in the soft handover region.
[0063] Referring to FIG. 4, a new radio link is established between
the active set Node B 125 and the UE 130 in steps 401 to 405 in the
same manner as steps 301 to 305 of FIG. 3. Upon completed setup of
a lub transmission line with the active set Node B 125 in step 405,
the SRNC 121 is ready for user data transmission to the active set
Node B 125. No transmission line synchronization is needed for the
HS-DSCH. The transmission line synchronization is a process of
synchronizing the SRNC 121 and a Node B to a reference time. If the
SRNC 121 implements scheduling, the transmission line
synchronization is needed. However, the Node B is responsible for
scheduling, which obviates the need for the transmission line
synchronization.
[0064] In steps 406 and 407, the UE 130 and the SRNC 121 exchange
an Active Set Update message and an Active Set Update Complete
message. In these steps, they can determine the logical ID of the
best cell by agreement.
[0065] In accordance with the present invention, while multiple
cells may be members of the active set, only one of them transmits
and receives at any time, potentially decreasing interference and
increasing system capacity, as described above. The UE selects the
best cell for transmitting on the downlink. Though not shown in
FIG. 4, an FP 211 of the SRNC 121 continuously transmits data
frames including user data to the best cell Node B 123. While the
SRNC 121 transmits user data to all Node Bs with radio links
established with the UE 130 in the conventional FCS, it transmits
the user data only to the best cell Node B 123 on the radio link in
the present invention. Though no data is transmitted to the active
set Node Bs, the transmission lines are maintained between the
active set Node Bs and the SRNC 121 so that data frame transmission
can be carried out at any time when necessary. That is, the active
set Node B 125 maintains the lub transmission line with the SRNC
121 and in addition is informed of a scrambling code that
identifies the UE 130.
[0066] Data transmission according to the embodiment of the present
invention will be described below with reference to FIGS. 7 and
8.
[0067] FIG. 7 illustrates a data transmission procedure after the
transmission line is established between the Node B 125 and the
SRNC 121 in the case where the best cell is not changed.
[0068] Referring to FIG. 7, the UE transmits a BCI, a CQI, and
other information to the Node Bs 123 and 125 in step 701. The
active set cells have already known the scrambling code and
channelization code for the uplink transmission in step 402 of FIG.
4. Thus, the BCI is transmitted to all active set cell nodes and
the best cell Node B 123. The BCI is transmitted on a DPCCH and
contains the logical ID of the best cell which is determined based
on the measured radio link statuses of the cells. The radio link
status of a cell can be estimated by measuring the reception
strength of a CPICH received from the cell. The best cell logical
ID may be determined by agreement between the SRNC 121 and the UE
130 during an HS-DSCH set-up or in step 407 of FIG. 4. Aside from
the BCI, the DPCCH may include information as to whether user data
received on the HS-DSCH has errors or not (ACK/NACK) and the radio
link quality of the best cell. The active set Node B 125 then
checks whether the BCI indicates the Node B 125. If it does not,
the Node B 125 does not receive the other information. On the other
hand, if the BCI indicates the Node B 125, the Node B 125 transmits
information about its MCS level and a reception indicator based on
the CQI and the ACK to the UE 130. Since it is assumed that the
best cell is not changed, the BCI indicates the Node B 123. Upon
receipt of the BCI, the best cell Node B 123 determines an MCS to
be used and user data for transmission based on the CQI and the ACK
and transmits the CQI and a reception indicator to the UE 130 by
scheduling in step 702. The reception indicator indicates an action
time when the user data is to be transmitted. In step 703, the best
cell Node B 123 transmits the user data to the UE 130. The UE 130
determines whether the user data has errors and transmits a BCI,
CQI, and an ACK based on measurements of its PHY to the active set
Node B 125 in step 704. Steps 705 to 709 are a repetition of steps
701 to 704. In accordance with the present invention, no user data
exchange and inter-Node B buffer management are carried out between
the SRNC 121, the best cell Node B 123, and the active set Node B
125. The SRNC 121 transmits user data only to the best cell Node B
123 by the FP in step 710.
[0069] FIG. 8 illustrates a data transmission procedure after the
transmission line is established between the Node B 125 and the
SRNC 121 in the case where the best cell is changed. Here, an old
best cell node is the Node B 123 and a new best cell Node B is the
Node B 125.
[0070] Referring to FIG. 8, the UE transmits a BCI to the Node Bs
123 and 125 periodically in steps 801, 807 and 808. When the UE
determines to change the best cell from the Node B 123 to the new
best cell Node B 125, it transmits a BCI indicating the Node B 125
on the DPCCH to the Node Bs 123 and 125 in step 801. Since the Node
Bs 123 and 125 already known the scrambling code and channelization
code for the uplink transmission in step 402 of FIG. 4, they can
receive the BCI. Upon receipt of the BCI, the Node B 123 neglects
signals received after the BCI, discontinuing transmission of the
HS-DSCH to the UE 130. Meanwhile, the FP of the Node B 125
determines an MCS to be used based on a CQI received after the BCI,
preparing for data transmission on the downlink. In step 802, the
Node B 125 transmits a BSCI (Best Cell Switching Indicator) to the
SRNC 121, indicating the change of the best cell. The FP of the
SRNC 121 initiates transmission of data frames to the Node B 125,
discontinuing data transmission on the lub transmission line
between the Node B 123 and the SRNC 121 in step 804. The Node B 125
determines an MCS and a reception indicator based on the received
data frame and transmits the MCS information and the reception
indicator to the UE 130 by its PHY. Then the Node B 125 transmits
user data to the UE 130 through the MAC and PHY in step 806.
[0071] Meanwhile, the PHY of the UE 130 notifies its RLC of the BCI
transmission. If the RLC layer has operated in an AM (Acknowledged
Mode), it transmits an RLC STATUS PDU (Protocol Data Unit) message
on a DPDCH to the SRNC 121, providing information about its
reception status up to the best cell switching time point in step
803. The RLC of the SRNC 121 retransmits RLC PDUs that the UE has
not received yet through the Node B 123. Thus, the UE 130 can
receive all data using FCS even when the best cell is changed.
[0072] While the BCSI is transmitted from the FP of the Node B 125
to the SRNC 121, the SRNC 121 continues transmitting data frames to
the Node B123. The RLCs of the UE 130 and the SRNC 121 carry out
retransmission of data frames transmitted from the SRNC 121 from
step 802 to step 804. Therefore, the Node Bs 123 and 125 do not
need to have the data that has not been transmitted to the UE
yet.
[0073] As described with reference to FIGS. 4, 7 and 8, data
transmission only to the best cell Node B requires a novel RLC
operation and a novel FP.
[0074] In general, an RLC operates in an AM, UM (Unacknowledged
Mode), or TM (Transparent Mode). Only the AM and UM are available
in HSDPA. In the RLC UM, segmentation/assembly and
encryption/decryption of data received from a higher layer are
performed. In the RLC AM, segmentation/assembly,
encryption/decryption, and retransmission of data received from a
higher layer are performed. Here, retransmission in the RLC AM will
be described.
[0075] In the RLC AM, SDUs received from the higher layer are
segmented into RLC PDUs of a predetermined size, and the RLC PDUs
are sequentially numbered and then transmitted to a receiver. The
receiver memorizes the sequence numbers of defective RLC PDUs. If a
predetermined condition is satisfied, the receiver transmits the
SNs of the defective RLC to the transmitter by an RLC STATUS PDU.
The transmitter then transmits the RLC PDUs corresponding to the
SNs set in the RLC STATUS PDU. The predetermined condition can be a
time period set by a timer, or omission of some RLC PDUs. In the
present invention, the RLC of the UE can transmit the RLC STATUS
PDU only if it receives a primitive CPHY-NOTIFY from the PHY of the
UE. CPHY-NOTIFY functions to indicate the change of a best cell to
the RLC. When the PHY of the UE 130 decides to change the best cell
based on radio link quality measurements in step 801 of FIG. 8, its
PHY transmits the primitive CPHY-NOTIFY to the RLC. Then, the RLC
transmits the RLC STATUS PDU to the SRNC 121.
[0076] FIGS. 9A, 9B and 9C illustrate the architecture of the
HS-DSCH FP according to the embodiment of the present
invention.
[0077] Referring to FIGS. 9A, 9B and 9C, the FP handles a data
frame and a control frame. The FP data frame is used on the lub
interface, and the FP control frame transmits a BCSI according to
the present invention. The data frame delivers data received from a
higher layer of the FP and the control frame is used to perform an
original FP control functionality. The FP is defined as a transport
channel. A conventional transport channel takes charge of
scheduling and thus inserts scheduling information in the header of
a data frame. On the contrary, since a Node B performs HS-DSCH
scheduling, it is not necessary to insert related scheduling
information to the header of a data frame. Thus, timing and
channelization code information are not loaded in the data frame,
but MAC-h SDU information is loaded in the data frame.
[0078] Referring to FIG. 9A, the FP data frame is comprised of a
header and a plurality of MAC-h SDUs destined for a UE. Each row in
the data frame is one byte and reference numeral 910 denotes a
5-byte header. The header 910 includes Frame Type (FT) 911
indicating whether the frame is a control frame or a data frame,
MAC-h SDU Length 913 indicating the length of each SDU in the
payload, Spare Bits 914 and 917, NumOfSDU 915 indicating the number
of SDUs in the data frame, and Serial Number 918 being the ID of
the data frame. The Serial Number is an integer. The FT 911 is one
bit and the MAC-h SDU Length 913 is one byte. One data frame
accommodates SDUs of the same size. The Spare Bits 914 and 917 are
reserved for future use in relation to the MAC-h SDU Length 913 and
the SN 918, respectively. The NumbOfSDU 915 is one byte and the
last two bytes in the data frame are filled with payload CRC
(Cyclic Redundancy Check) 920.
[0079] FIG. 9B illustrates an FP control frame, i.e., a BCSI
control frame with a cell ID and timing information and FIG. 9C
illustrates an FP control frame, i.e., a BCSI control frame without
the cell ID and timing information. The Node B transmits a BCSI to
the FP of the SRNC, indicating that the best cell has been changed
so that the SRNC can transmit data to the new best cell Node B.
Since the SRNC knows the cell ID, the cell ID may not be needed.
However, to help the FP of the SRNC to take an appropriate action,
the cell ID can be inserted. For example, a corresponding transport
line ID such as an AAL2/ATM path identifier can be inserted in that
position. Considering data transmission starts to the new best cell
Node B when the SRNC receives the BCI, the timing information is
not necessary. However, the timing information can also be
transmitted for a future optional use. The most important
information that the BCSI delivers is the change of the best cell.
The information can be provided simply by indicating the type of a
control frame, i.e., a BCSI control frame without any other
additional information. Accordingly, the control frame can be
formatted as illustrated in FIG. 9C.
[0080] FIG. 10 illustrates the structure of an RNC for transmitting
an HS-DSCH FP according to the embodiment of the present invention.
Referring to FIG. 10, a transmission buffer 1001 temporarily stores
user data received from a MAC-c/sh until it is accumulated to one
data frame. The size of a data frame is not limited and determined
by the number of MAC-h SDUs received at one time and the size of
each SDU. When the transmission buffer 1001 has data enough to
construct a data frame, it outputs the data to a header and trailer
inserter 1002. The header and trailer inserter 1002 adds a header
and a trailer to the received data. The trailer is a 2-byte payload
CRC placed at the end of the format illustrated in FIG. 9A. The
trailer is determined by CRC operation of MAC-h SDU 1 to MAC-h SDU
n of FIG. 9A. Information to be filled in the header is provided by
an FP controller 1006. A multiplexer (MUX) 1003 scrambles a control
frame received from the FP controller 1006 and the data frame
received from the header and trailer inserter 1002 in an order
determined by the FP controller 1006. When both the header and
trailer inserter 1002 and the FP controller 1006 have transmission
data, it is determined which data has priority. The data frame
output from the MUX 1003 is transmitted to a receiving Node B
through a switching unit 1004.
[0081] A control frame received from the Node B is input to a CRC
checker 1005 through the switching unit 1004. The CRC checker 1005
checks a header CRC from the received data and if no errors are
detected in the data, it outputs the data to the FP controller
1006. Since no data delivery from the Node B to the RNC is defined
in the HS-DSCH FP, reception of a data frame from the Node B is not
considered.
[0082] FIG. 11 is a block diagram of the FP controller 1006
illustrated in FIG. 10.
[0083] Referring to FIG. 11, a control information distributor 1101
distributes control information 1007 received from the MAC-c/sh to
a buffer manager 1102, a header controller 1103, and a control
frame controller 1104. The control information 1107 includes
information about the number of MAC-h SDUs, the size of each MAC-h
SDU, and the amount of non-transmitted data remaining in the RLC
buffer. The information about the number of MAC-h SDUs and the size
of each MAC-h SDU is provided to the buffer manager 1102 and the
header controller 1103, and the amount of the data remaining in the
RLC buffer, to the control frame controller 1104. The buffer
manager 1102 indicates a time when data stored in the transmission
buffer 1001 is output to the header and trailer inserter 1002 based
on the received control information. The header controller 1103
constructs header information for a data frame using the received
control information. The control frame controller 1104 transmits a
Capacity Request control frame to a Node B using the received
control information when necessary. Upon receipt of a Capacity
Allocation control frame 1008, the control frame controller 1104
delivers it to the MAC-c/sh. The switching controller 1105 controls
connection between the RNC to Node Bs. As described before, the
SRNC establishes transmission lines with the Node Bs by ALCAP in
step 405 of FIG. 4. The transmission lines are AAL2/ATM. Then the
switching controller 1105 receives the IDs of the Node Bs that have
established the transmission lines by the Capacity Allocation
control frame 1008. The switching controller 1105 adds the IDs of
the Node Bs except the best cell Node B to an ASB (Active Set Node
B). The switching controller 1105 controls the switching unit 1004
to maintain only the connection with the best cell Node B. Upon
receipt of a BSCI control frame, the control frame controller 1104
transmits the ID of the new best cell to the switching controller
1105. The switching controller 1105 then updates the best cell Node
B and reestablishes the connection. Referring to FIG. 4, the Node B
125 transmits the BCSI control frame and the control frame
controller 1104 transfers it to the switching controller 1105. The
switching controller 1105 controls the switching unit 1004 to
release the connection from the Node B 123 and establishes a
connection with the Node B 125. Since AAL2/ATM connections have
already been made with the Node Bs 123 and 125, the above
connection release and establishment means internal connection in
the switching unit 1004.
[0084] FIG. 12 is a block diagram for a node B for transmitting
user data by the FP in the HSDPA mobile communication system
according to the embodiment of the present invention. Upon receipt
of a frame from a lower layer through an AAL2/ATM transmission line
1204, a demultiplexer (DEMUX) 1200 routs the frame to a header
remover 1201 or an FP controller 1202 according to an FP field of
its header (1205, 1206). The header remover 1201 removes the header
from the data frame and outputs header information to the FP
controller 1202 (1207). The FP controller 1202 transmits the header
information to the MAC-h (1208). The header remover 1201
additionally checks errors in the data frame by operating a header
CRC and a payload CRC. If errors are found, the data frame is
discarded and if no errors are found, the payload is routed to the
MAC-h. Reference numerals 1208 denotes information directed from
the MC-h to the FP controller 1202 as needed to construct a control
frame but not defined in the present invention. Reference numeral
1209 denotes the header information directed from the FP controller
1202 to the MAC-h. Reference numeral 1210 denotes information
directed from the PHY of the node B to the FP controller 1202,
indicating that the best cell has been changed. Upon receipt of the
control information 1210, the FP controller 1202 transmits the RNC
a BCSI control frame with a CRC added in a CRC adder 1203 via the
AAL2/ATM line. As compared to the conventional technology, the RNC
FP illustrated in FIGS. 10 and 11 can transmit user data only to
the best cell node B and the node B FP illustrated in FIG. 12, upon
recognizing the change of the best cell, can notify the RNC FP of
the best cell change.
[0085] FIG. 13 is a flowchart illustrating a user data transmission
method in a UE in the HSDPA mobile communication system according
to the embodiment of the present invention. The following
description is made with the appreciation that the best cell Node B
is the Node B 123 and an active cell Node B is the Node B 125.
[0086] Referring to FIG. 13, the UE 130 measures the channel
statuses CQ(A) and CQ(B) of the Node Bs 123 and 125 in step 1301.
The UE compares the channel status CQ(A) and CQ(B) in step 1302. If
CQ(A) is better than CQ(B), the UE 130 transmits a BCI indicating
the Node B 123 on a DPCCH to the Node Bs 123 and 125 in step 1303.
On the other hand, if CQ(B) is better than CQ(A), the UE 130
transmits a BCI indicating the Node B 125 on the DPCCH to the Node
Bs 123 and 125 in step 1304. The UE 130 transmits CPHY-NOTIFY to
its RLC, indicating the switching of the best cell in step 1305.
The RLC of the UE 130 transmits an RLC STATUS PDU to the SRNC 121
on a DPDCH in step 1306. The RLC of the SRNC 121 then retransmits
RLC PDUs that have not been transmitted to the UE 130 based on the
RLC STATUS PDU.
[0087] FIG. 14 is a flowchart illustrating a user data transmission
method in a Node B in the HSDPA mobile communication system
according to the embodiment of the present invention.
[0088] Referring to FIG. 14, the Node B 123 or 125 monitors the
DPCCH from the UE 130 periodically in step 1401. Upon receipt of
the DPCCH, the Node B detects a BCI from the DPCCH and extracts a
cell ID from the BCI. If the BCI does not indicate the Node B, the
Node B neglects signals after the BCI, i.e., a CQI and an ACK/NACK
and returns to step 1401. If the BCI indicates the Node B, the Node
B recognizes that it has been selected as the best cell in step
1403. The Node B checks whether its transmission buffer has data to
be transmitted. In the absence of transmission data, the Node B
goes to step 1404 and in the presence of transmission data, it goes
to step 1405. In step 1404, the Node B transmits a BCSI to the SRNC
121, indicating that it has been selected as the best cell and
returns to step 1401. In step 1405, the Node B decides an MCS for
the downlink transmission and schedules the buffered data and
transmits control information including the BCI on a DPCCH in step
1406. The Node B transmits data on the HS-DSCH in step 1407.
[0089] FIG. 15 is a flowchart illustrating a user data transmission
method in an SRNC in the HSDPA mobile communication method
according to the embodiment of the present invention.
[0090] Referring to FIG. 15, the SRNC 121 transmits an FP when it
has a data frame to be transmitted in step 1501 and checks whether
an MR including the channel status information of the Node Bs 123
and 125 has been received from the UE 130 in step 1502. Upon
receipt of the MR, the SRNC 121 determines whether to establish a
new radio link in step 1503. In the case of establishing a new
radio link, the SRNC 121 transmits a Radio Link Setup Request
message to the active set Node B 125 of FIG. 1 in step 1504 and
determines whether a Radio Link Setup Response message has been
received from the Node B 125 in step 1505. Upon receipt of the
Radio Link Setup Response message, the SRNC 121 establishes a lub
transmission line with the active set Node B 125 by ALCAP in step
1506 and adds the ID of the active set Node B 125 to the ASB in
step 1507. If the MR is not received in step 1502, the SRNC 121
determines whether a BCSI has been received from a particular Node
B in step 1508. Upon receipt of the BCSI from the particular Node
B, the SRNC 121 determines whether the particular Node B is
identical to a Node B set as a best cell Node B in step 1509. If
they are different, the SRNC 121 updates the best cell Node B in
step 1510 and switches the transmission line to the new best cell
Node B.
[0091] As described above, transmission of an FP data frame only to
the best cell Node B according to the present invention has the
following advantages.
[0092] (1) lub transmission resources and the buffer resources of
active set Node Bs can be used more efficiently;
[0093] (2) RLC retransmission requests can be minimized by allowing
a Node B to rapidly report the change of the best cell to the FP of
an SRNC; and
[0094] (3) When the best cell is changed, an RLC retransmission
request is rapidly transmitted, thereby efficiently managing the
RLC buffer of a UE.
[0095] While the invention has been shown and described with
reference to a certain preferred embodiment thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims.
* * * * *